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[205.151.56.5]) by smtp.gmail.com with ESMTPSA id d190sm1061823qkf.103.2021.04.20.20.29.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Apr 2021 20:29:23 -0700 (PDT) From: Maxim Cournoyer To: Mark H Weaver Subject: Re: Implications of QEMU binfmt transparent emulation for builds References: <87eegsnexv.fsf@cbaines.net> <87wnujzqyo.fsf@netris.org> Date: Tue, 20 Apr 2021 23:29:22 -0400 In-Reply-To: <87wnujzqyo.fsf@netris.org> (Mark H. Weaver's message of "Sat, 06 Mar 2021 20:34:28 -0500") Message-ID: <877dkwe2nh.fsf@gmail.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=2607:f8b0:4864:20::729; envelope-from=maxim.cournoyer@gmail.com; helo=mail-qk1-x729.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: guix-devel@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "Development of GNU Guix and the GNU System distribution." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: guix-devel@gnu.org Errors-To: guix-devel-bounces+larch=yhetil.org@gnu.org Sender: "Guix-devel" X-Migadu-Flow: FLOW_IN ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=yhetil.org; s=key1; t=1618975776; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references:list-id:list-help:list-unsubscribe: list-subscribe:list-post:dkim-signature; bh=eZimzkXUVoqfXp+4Gk/hMCDbTt7x9ibbk3YT4AMFpuM=; b=VIbVKSpPbzF/xy7ptogf5Als3OOruIPyyGk9SCtQAFmOxBSf/SXqUp34fGZ1ePeGILOIY1 6P1N2Jvqx3ME+zX2/vMBMx7rKi6dvGwXDxmTgS0sT+O6znR1Y9kHGUWlfXblSVN1Tkdu21 B4OBoqNeV5KN0G+nuaKKB7WcraYov1+qiEZdjMv9XKG9xBsHM3QpWLPSSfvC2MJrSoyquU VHjynIP1wGSvr49BEQms0Z/Oriz+djI54i1DMwhtAMvmH5fz+M+qiDCsIlphnGjK0N/gEd XM/wulWILFmDuFlFnTyjNqdDtq+JlHeBi/C6JoyO9Q/S94T7OOdB7QMWwuLWtA== ARC-Seal: i=1; s=key1; d=yhetil.org; t=1618975776; a=rsa-sha256; cv=none; b=qSpUecboWjeo+B0HUxQw5TOZsixEWau7R/RBIGQZnmto3q8MAvzpC+nqCeXG++NID9XOKp xPBngKepQkmFTIQhZMQ7skaRMeXKXukBrlUo5qhUOXw9/CGiXav58UO6ORMESSFwzQG2VY YqJvShGTckl9MLSCqQVh/RddwOpvRysCHhMAoW75OAwjNdDx5l9D/9160id09ba9GSZkxv EtqlM8rGNt6+g6GdodlM2AmfGeYZ14YQDHcSWDzGc78zKc4ETXximSXbFrjcY+D8Jo3FdG FgSS2P8aiGZL67/RsaLQ3AZVBu0kgSwn+wJh63S0NNB29gWSxYaxec4A9zOjtw== ARC-Authentication-Results: i=1; aspmx1.migadu.com; dkim=fail ("headers rsa verify failed") header.d=gmail.com header.s=20161025 header.b=lnhVWPB8; dmarc=fail reason="SPF not aligned (relaxed)" header.from=gmail.com (policy=none); spf=pass (aspmx1.migadu.com: domain of guix-devel-bounces@gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=guix-devel-bounces@gnu.org X-Migadu-Spam-Score: -1.34 Authentication-Results: aspmx1.migadu.com; dkim=fail ("headers rsa verify failed") header.d=gmail.com header.s=20161025 header.b=lnhVWPB8; dmarc=fail reason="SPF not aligned (relaxed)" header.from=gmail.com (policy=none); spf=pass (aspmx1.migadu.com: domain of guix-devel-bounces@gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=guix-devel-bounces@gnu.org X-Migadu-Queue-Id: E2F52B642 X-Spam-Score: -1.34 X-Migadu-Scanner: scn0.migadu.com X-TUID: P4Gbpw795dVX Hello Mark, Mark H Weaver writes: > Hi Christopher, > > Christopher Baines writes: > >> I'm starting to play with mixing native and emulated builds with the >> Guix Build Coordinator again. I did do this many months ago, but at that >> time, there wasn't support for targeting retries across a range of >> machines, to help avoid blockages due to QEMU issues. >> >> Anyway, something that's been on my mind regarding QEMU and builds is >> how well this matches up with building natively. > > Here's one significant problem with emulated builds, although perhaps > not the kind of problem you were asking about: > > Due to differences in the memory models of Intel and other systems such > as ARM, it is easy to write multithreaded code that works robustly on > Intel systems but sporadically fails on other architectures such as ARM. > > However, an ARM emulator running on an Intel system will effectively use > an Intel memory model, because it would be prohibitively expensive to > faithfully simulate the ARM memory model on Intel hardware, and the only > benefit would be to demonstrate bugs that can't happen on Intel systems. > > Therefore, test suites run under an emulator will almost certainly fail > to find architecture-specific thread safety problems, which I expect are > among the most important tests to be done, and among the most likely to > otherwise go unnoticed. > > For this reason, I suggest that we should avoid emulated builds in our > build farm. Very interesting; thanks for sharing this great piece of information! I had no idea about this simplification/shortcut used by QEMU. Maxim